Assessing ecological and molecular divergence between the closely related species Hydrolagus pallidus and H. affinis (Chimaeridae).

This study investigated taxonomic validity of the pale ghost shark Hydrolagus pallidus Hardy & Stehmann, 1990, which was described as a species distinct from the smalleyed rabbitfish H. affinis (de Brito Capello 1868). While few morphological characters distinguish the two taxa, a striking difference in sex ratio and fixed differences (1·1-1·6% divergence) in the cytochrome oxidase subunit I barcoding gene support the recognition of both species.

Comparative evaluation of potential indicators and temporal sampling protocols for monitoring genetic erosion.

Genetic biodiversity contributes to individual fitness, species' evolutionary potential, and ecosystem stability. Temporal monitoring of the genetic status and trends of wild populations' genetic diversity can provide vital data to inform policy decisions and management actions. However, there is a lack of knowledge regarding which genetic metrics, temporal sampling protocols, and genetic markers are sufficiently sensitive and robust, on conservation-relevant timescales. Here, we tested six genetic metrics and various sampling protocols (number and arrangement of temporal samples) for monitoring genetic erosion following demographic decline. To do so, we utilized individual-based simulations featuring an array of different initial population sizes, types and severity of demographic decline, and DNA markers [single nucleotide polymorphisms (SNPs) and microsatellites] as well as decline followed by recovery. Number of alleles markedly outperformed other indicators across all situations. The type and severity of demographic decline strongly affected power, while the number and arrangement of temporal samples had small effect. Sampling 50 individuals at as few as two time points with 20 microsatellites performed well (good power), and could detect genetic erosion while 80-90% of diversity remained. This sampling and genotyping effort should often be affordable. Power increased substantially with more samples or markers, and we observe that power of 2500 SNPs was nearly equivalent to 250 microsatellites, a result of theoretical and practical interest. Our results suggest high potential for using historic collections in monitoring programs, and demonstrate the need to monitor genetic as well as other levels of biodiversity.

Evolution of population genetic structure of the British roe deer by natural and anthropogenic processes (Capreolus capreolus).

Human influence typically impacts on natural populations of conservation interest. These interactions are varied and sometimes complex, and may be negative and unintended or associated with conservation and management strategy. Understanding the details of how these interactions influence and are influenced by natural evolutionary processes is essential to the development of effective conservation strategies. In this study, we investigate a species in Britain that has experienced both negative impact through overhunting in historical times and management efforts through culls and translocations. At the same time, there are regional populations that have been less affected by human influence. We use mtDNA and nuclear microsatellite DNA markers to investigate patterns of connectivity and diversity and find multiple insular populations in Britain that probably evolved within the Holocene (when the habitat was free of ice). We identify three concurrent processes. First, surviving indigenous populations show highly provincial patterns of philopatry, maintaining and generating population structure on a small geographic scale. Second, founder populations into habitat extirpated of native populations have expanded, but remained largely insular. Third, introductions into established populations generate some admixture. We discuss the implications for the evolution of diversity of the integration of natural processes with anthropogenic influences on population size and distribution.

Local selection and population structure in a deep-sea fish, the roundnose grenadier (Coryphaenoides rupestris).

Local populations within a species can become isolated by stochastic or adaptive processes, though it is most commonly the former that we quantify. Using presumably neutral markers we can assess the time-dependent process of genetic drift, and thereby quantify patterns of differentiation in support of the effective management of diversity. However, adaptive differences can be overlooked in these studies, and these are the very characteristics that we hope to conserve by managing neutral diversity. In this study, we used 16 hypothetically neutral microsatellite markers to investigate the genetic structure of the roundnose grenadier in the North Atlantic. We found that one locus was a clear outlier under directional selection, with F(ST) values much greater than at the remaining loci. Differentiation between populations at this locus was related to depth, suggesting directional selection, presumably acting on a linked locus. Considering only the loci identified as neutral, there remained significant population structure over the region of the North Atlantic studied. In addition to a weak pattern of isolation by distance, we identified a putative barrier to gene flow between sample sites either side of the Charlie-Gibbs Fracture Zone, which marks the location where the sub-polar front crosses the Mid-Atlantic Ridge. This may reflect a boundary across which larvae are differentially distributed in separate current systems to some extent, promoting differentiation by drift. Structure due to both drift and apparent selection should be considered in management policy.

Bathymetric barriers promoting genetic structure in the deepwater demersal fish tusk (Brosme brosme).

Population structuring in the North Atlantic deepwater demersal fish tusk (Brosme brosme) was studied with microsatellite DNA analyses. Screening eight samples from across the range of the species for seven loci revealed low but significant genetic heterogeneity (F(ST) = 0.0014). Spatial genetic variability was only weakly related to geographical (Euclidean) distance between study sites or separation of study sites along the path of major ocean currents. Instead, we found a significant effect of habitat, indicated by significant differentiation between relatively closely spaced sites: Rockall, which is surrounded by very deep water (>1000 m), and the Mid-Atlantic Ridge, which is separated from the European slope by a deep ocean basin, were differentiated from relatively homogeneous sites across the Nordic Seas. Limited adult migration across bathymetric barriers in combination with limited intersite exchange of pelagic eggs and larvae due to site-specific circulatory retention or poor survival during drift phases across deep basins may be reducing gene flow. We regard these limitations to gene flow as the most likely mechanisms for the observed population structure in this demersal species. The results underscore the importance of habitat boundaries in marine species.